Bug CESM1.2.0 when using branch with BRNCH_RETAIN_CASENAME=TRUE

I believe there is a bug in CESM when you set a branch run with BRNCH_RETAIN_CASENAME=TRUE(Note this only happens when BRNCH_RETAIN_CASENAME=TRUE. I can run if I change the casename but I would like to keep the same casename).

To demonstrate the problem, I did a very simple experiment. I ran a 5-day run. Then I branched from the end of the run with BRNCH_RETAIN_CASENAME=TRUE The first submission of the branch run worked fine, but when the model resubmitted, it crashed with the follwing error: